Java Inheritance Tutorial

What is Inheritance?

Inheritance in Java is a mechanism in which one object acquires all the properties and behaviors of a parent object. It is an important part of Object-Oriented Programming (OOPs).

Superclass (Parent): The class whose features are inherited.
Subclass (Child): The class that inherits the features of the superclass.
Key Keyword: The extends keyword is used to inherit a class.
Primary Benefits: Code reusability and method overriding (Runtime Polymorphism).

Types of Inheritance in Java

1. Single Inheritance Supported

In single inheritance, a subclass inherits features from a single superclass. It creates a simple 1-to-1 parent-child hierarchy.

// Superclass
class Animal {
    void eat() { System.out.println("Eating..."); }
}

// Subclass inheriting from Animal
class Dog extends Animal {
    void bark() { System.out.println("Barking..."); }
}

2. Multilevel Inheritance Supported

In multilevel inheritance, a class extends another class, which is already extending another class, forming a chain of inheritance.

class Animal {
    void eat() { System.out.println("Eating..."); }
}

class Dog extends Animal {
    void bark() { System.out.println("Barking..."); }
}

// Inherits properties from both Dog and Animal
class BabyDog extends Dog {
    void weep() { System.out.println("Weeping..."); }
}

3. Hierarchical Inheritance Supported

In hierarchical inheritance, multiple subclasses inherit from a single superclass.

class Animal {
    void eat() { System.out.println("Eating..."); }
}

class Dog extends Animal {
    void bark() { System.out.println("Barking..."); }
}

class Cat extends Animal {
    void meow() { System.out.println("Meowing..."); }
}

4. Multiple Inheritance Via Interfaces Only

Multiple inheritance occurs when a subclass extends more than one parent class. Java does not support this using classes to avoid ambiguity (the "Diamond Problem"), but supports it via Interfaces.

interface Printable {
    void print();
}

interface Showable {
    void show();
}

// Implementing multiple interfaces using the 'implements' keyword
class Document implements Printable, Showable {
    public void print() { System.out.println("Printing..."); }
    public void show() { System.out.println("Showing..."); }
}

5. Hybrid Inheritance Via Interfaces Only

Hybrid inheritance is a combination of two or more types of inheritance. Since it involves multiple inheritance, it is only achieved through Interfaces in Java.

class Grandparent {}

interface Parent1 {}
interface Parent2 {}

// Combining Single + Multiple Inheritance
class Child extends Grandparent implements Parent1, Parent2 {
    // Implementation
}